Planar and vertical organic field effect transistors are electrical elements known from semiconductor technologies. The function of both kinds of transistors is very similar, but the transistors are different in their geometry. In the planar OFET, three electrodes (gate electrode, source electrode and drain electrode) are arranged according to the conventional concept of the transistor. The source electrode and the drain electrode are arranged opposite to each other, wherein the gate electrode is arranged above or below the source electrode and the drain electrode. In the VOFET, all three electrodes are arranged on top of each other in a stacked manner.
The function of both transistor concepts is described in the following: Between the source electrode (also called the source) and the drain electrode (also called the drain) flows a current which is controlled by the gate electrode (also called the gate) via an electrical voltage. In contrast to the planar OFET, the current flows in the VOFET in a vertical channel between the source and the drain. Both concepts are also known in conventional silicon technology. Using organic materials in the transistors lead to the advantage of cheaper materials and a potential application on flexible substrates. Essential criteria for an organic device are high current densities at low on-set voltages and a high ratio between ON current and OFF current. In particular, the ON current can be improved by inserting dopants adjacent to the source electrode and/or the drain electrode.
In a previous application EP 2 784 839 A1, incorporated herein by the reference, it was shown that inserting the organic compound F6-TCNNQ as contact dopant between the electrodes (source and/or drain) and a semiconducting material improves the injection of charge carriers in an organic transistor.